Vehicle restraints are used to restrain transport vehicles from moving away from loading docks. Typical vehicle restraints are hooks or barriers that engage the rear impact guard (“RIG”), also known as an ICC bar, of a transport vehicle. Commercial examples of this type of device are the Rite-Hite ADL series, the Kelley Star series and the Serco SL series of vehicle restraints.
Actuation of vehicle restraints can be accomplished electromechanically and hydraulically. Power Ramp “Power Hook II”, the Kelley “Hidden Hook” and the Serco “SLP 2000” are commercial products that use hydraulic cylinders to position the vehicle restraint. Although electromechanical actuation of the retractable hook can lower cost, a vehicle restraint which retracts the hook hydraulically can allow the hook to retract in the operative position to reduce the distance or “running room” that the transport vehicle can move away from the dock while the restraint has engaged a vehicle. However the hydraulic control circuits of commercially available retractable-hook vehicle restraints are complex and costly.
An example of a hydraulic control circuit for a retractable hook vehicle restraint is shown in FIG. 5. The hydraulic circuit, which includes six valves, is complex and costly. The hydraulic circuit also predominately utilizes spool valves, which have a relatively high leakage rate. Consequently, pressure may drop relatively quickly over time, thereby loosening the vehicle restraint's hold on the vehicle, or else causing the pump to run frequently to maintain pressure.
Accordingly, there is a need for an apparatus and method for controlling vehicle restraints, which can be configured on a simplified branch circuit. There is also a need for an apparatus and method for more effectively and/or efficiently restraining a vehicle from moving away from a loading dock.